Reflective plate, production method therefor, liquid crystal device, and electronic device

ABSTRACT

The invention provides a thin reflective plate having cholesteric liquid crystal that can prevent or reduce a decrease of reflection efficiency. A reflective plate includes a cholesteric liquid crystal layer, and the cholesteric liquid crystal layer includes a plurality of regions in which the helical axes of the cholesteric liquid crystal are aligned in different directions in the plane of a substrate, and therefore, the regions can reflect color light components having different wavelengths. Consequently, the cholesteric liquid crystal layer can reflect light formed of light components of different colors (for example, white light) as a whole. When the reflective plate is applied to a reflective liquid crystal display device or the like, it is possible to appropriately reflect white light for display.

This is a Division of application Ser. No. 10/351,506 filed Jan. 27,2003. The entire disclosure of the prior application is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a reflective plate and a productionmethod therefor, a liquid crystal device, and an electronic device. Moreparticularly, the invention relates to a reflective plate having acholesteric liquid crystal layer and a production method therefor, aliquid crystal device having the reflective plate, and an electronicdevice having the liquid crystal device.

2. Description of Related Art

The related art includes cholesteric reflective plates using cholestericliquid crystal. Liquid crystal molecules form periodic helicalstructures at a fixed pitch in the cholesteric liquid crystal, and thecholesteric liquid crystal has the property of selectively reflecting alight component of incident light having a wavelength corresponding tothe helical pitch and the refractive index. Therefore, the use of areflective plate having such cholesteric liquid crystal makes itpossible to provide a liquid crystal device which can selectivelyreflect a light component of incident light having a specificwavelength.

SUMMARY OF THE INVENTION

Some reflective plates using such cholesteric liquid crystal achieve areflective display that is close to white by stacking three layershaving different helical pitches corresponding to the wavelengths ofcolors, such as red, green, and blue. In this case, since a plurality oflayers are stacked, the layer thickness is increased, and the size ofthe reflective plate itself is increased. Moreover, for example, sincelight is absorbed by liquid crystal molecules until it reaches thelowermost layer, the reflection efficiency is decreased. Furthermore,since the number of production processes is increased by stacking, thecost may be increased.

The present invention addresses or solves the above and/or otherproblems, and provides a thin reflective plate having cholesteric liquidcrystal that can prevent or reduce a decrease of reflection efficiency,and a production method therefore. The invention also provides a liquidcrystal device using the reflective plate and an electronic devicehaving the liquid crystal device.

In order to address or achieve the above, a reflective plate of thepresent invention is provided such that a cholesteric liquid crystallayer is formed on a substrate, and the helical axes of cholestericliquid crystal in the cholesteric liquid crystal layer are aligned indifferent directions at least in a substrate plane.

The reflective plate having the cholesteric liquid crystal layer canreflect color light having a wavelength corresponding to the helicalpitch of the helical structure formed by the cholesteric liquid crystal.In the present invention, the helical axes of the helical structuresformed by the cholesteric liquid crystal in the cholesteric liquidcrystal layer are aligned in different directions at least in thesubstrate plane, and the helical pitch viewed from the directionperpendicular to the substrate plane differs among the regions in whichthe helical axes are aligned in different directions. Therefore, thewavelength of the reflected color light from the reflective plate viewedfrom the direction perpendicular to the substrate plane differs amongthe regions in which the helical axes are aligned in differentdirections, that is, light formed of light components of differentcolors (for example, white light) can be reflected. For example, whenthe reflective plate is applied to a reflective display device, whitelight can be appropriately reflected for display. In the presentinvention, light of mixed color (for example, white light) is notreflected by stacking cholesteric liquid crystal layers, and instead isreflected by forming, in the substrate plane, a plurality of regions inwhich the helical axes are aligned in different directions. Therefore,the cholesteric liquid crystal layer, and the reflected plate can bemade of a thin film, and this enhances the thickness uniformity.Furthermore, in the present invention, since the helical axes of thehelical structures formed by the cholesteric liquid crystal are alignedin various directions in the substrate plane, the distribution of therefractive index is increased, and reflected light can be scatteredwithout providing a separate scattering layer.

The cholesteric liquid crystal layer may include at least two of acholesteric liquid crystal region in which the helical axes are alignedsubstantially perpendicularly to the substrate plane, a cholestericliquid crystal region in which the helical axes are alignedsubstantially parallel to the substrate plane, and a cholesteric liquidcrystal region in which the helical axes tilt at a predetermined angleto the substrate plane. In this case, since at least two of thecholesteric liquid crystal regions in which the helical axes are alignedperpendicularly to, tilt relative to, and are aligned parallel to thesubstrate plane are included, at least two types of color components canbe reflected by these regions, and therefore, light of mixed colorcontaining a plurality of colors can be reflected. In particular, whenall of the three cholesteric liquid crystal regions are included, colorlight that is closer to white can be reflected, and the reflective platethat can reflect white light is suitably used for a reflective displaydevice.

More specifically, a helical-axis-direction aligning device may beprovided so as to align the helical axes of the cholesteric liquidcrystal in different directions in the substrate plane. In this case,the helical-axis-direction aligning device allows the helical axes ofthe helical structures formed by the cholesteric liquid crystal to bealigned in different directions at least in the substrate plane. Morespecifically, an alignment layer capable of aligning cholesteric liquidcrystal may be formed as the helical-axis-direction aligning devicebetween the substrate and the cholesteric liquid crystal layer, and maybe locally formed in the substrate plane. In this case, by locallyforming the alignment layer in the substrate plane, the alignment stateof the cholesteric liquid crystal differs between a region in which thealignment layer is formed and a region in which the alignment layer isnot formed. Therefore, it is possible at least to form regions in whichthe helical axes of the helical structures formed by the cholestericliquid crystal are aligned in different directions. The alignment layermay be formed, for example, by rubbing a polyimide film.

An alignment layer that is capable of aligning the cholesteric liquidcrystal may be formed as the helical-axis-direction aligning devicebetween the substrate and the cholesteric liquid crystal layer, and mayinclude a homeotropic alignment layer and a homogeneous alignment layer,and the homeotropic alignment layer and the homogeneous alignment layermay be in contact with the cholesteric liquid crystal layer. In thiscase, the alignment state of the cholesteric liquid crystal differsbetween a cholesteric liquid crystal region in contact with thehomeotropic alignment layer and a cholesteric liquid crystal region incontact with the homogeneous alignment layer, and therefore, thedirection of the helical axes of the helical structures formed by thecholesteric liquid crystal also differs between the liquid crystalregions.

The homeotropic alignment layer and the homogeneous alignment layer maybe made of an alignment film formed, for example, by rubbing a polyimidefilm, and can be respectively obtained by using different kinds ofpolyimides. More specifically, it is preferable to use polyimides havingdifferent side chains of polyimide molecules. For example, by changingthe direction of the above-described rubbing, the respective alignmentlayers can be obtained. For example, the homeotropic alignment layer mayrefer to an alignment layer in which the pretilt angle is relativelylarge, and the homogeneous alignment layer may refer to an alignmentlayer in which the pretilt angle is relatively small.

An alignment layer that is capable of aligning the cholesteric liquidcrystal may be formed as the helical-axis-direction aligning devicebetween the substrate and the cholesteric liquid crystal layer, and mayhave irregularities on its surface along the border with the cholestericliquid crystal layer. In this case, the cholesteric liquid crystal is incontact with the irregularities formed on the alignment layer, thehelical axes of the helical structures formed by the cholesteric liquidcrystal tilt in various directions with respect to the substrate planedepending on the inclinations of the irregularities, and a plurality ofregions in which the helical axes are aligned in different directionsare formed in the substrate plane. By forming irregularities on thesubstrate surface, irregularities can be formed on the alignment layerplaced between the substrate and the cholesteric liquid crystal layer.For example, irregularities can be formed on the alignment layer byforming an acrylic layer on the substrate and forming irregularities onthe acrylic layer.

The helical-axis-direction aligning device may be a filler charged inthe cholesteric liquid crystal layer. In this case, the alignment stateof the cholesteric liquid crystal differs between a portion that ischarged with the filler and a portion that is not charged with thefiller, and therefore, the helical axes of the helical structures formedby the cholesteric liquid crystal are aligned in different directionsbetween the charged portion and the uncharged portion. The filler maybe, for example, resin or glass beads or fibers. The surface of thefiller may be subjected to homeotropic surface treatment, and thecholesteric liquid crystal can be aligned in a plurality of directionson the surface of the filler by such homeotropic surface treatment.Furthermore, by making the filler substantially spherical, thecholesteric liquid crystal can be aligned in more directions by thesubstantially spherical surface, and the direction of the helical axesof the cholesteric liquid crystal can more reliably differ between thecharged portion and the uncharged portion.

A reflective-plate production method of the present invention includesforming a cholesteric liquid crystal layer on a substrate. Thecholesteric liquid crystal layer forming step includes applying acholesteric liquid crystal monomer, and polymerizing the appliedcholesteric liquid crystal monomer. In the monomer application step, thecholesteric liquid crystal monomer is applied in an isotropic state, andis then supercooled.

Such a production method makes it possible to obtain the above-describedreflective plate of the present invention having the cholesteric liquidcrystal layer including a plurality of regions in which the helical axesof the cholesteric liquid crystal are aligned in different directions inthe substrate plane. That is, when the cholesteric liquid crystalmonomer in an isotropic state is supercooled, it partially remains inthe isotropic state. By polymerizing the monomer, a cholesteric liquidcrystal layer in which the orientation has a given distribution can beformed. Therefore, a plurality of regions in which the helical axes arealigned in different directions are formed in the cholesteric liquidcrystal layer. In this case, in the monomer application step, thecholesteric liquid crystal monomer is applied at a temperature higherthan or equal to the temperature T₁ at which it has an isotropic phase,more specifically, at approximately (T₁+30°), and is then supercooled toa temperature lower than or equal to T₁, more specifically,approximately (T₁−30°). The cholesteric liquid crystal monomer in thisspecification refers to a monomer that can have a cholesteric liquidcrystal phase by polymerization. In the above monomer polymerizing step,the applied cholesteric liquid crystal monomer may be polymerized byultraviolet irradiation or heating.

A reflective-plate production method of the present invention includesforming a cholesteric liquid crystal layer on a substrate. Thecholesteric liquid crystal layer forming step includes at least applyinga cholesteric liquid crystal monomer, and polymerizing the appliedcholesteric liquid crystal monomer by ultraviolet irradiation. In themonomer polymerizing step, the ultraviolet dose has a distribution inthe substrate plane when ultraviolet irradiation is performed. Such aproduction method makes it possible to obtain the above-describedreflective plate of the present invention having the cholesteric liquidcrystal layer including a plurality of regions in which the helical axesof the cholesteric liquid crystal are aligned in different directions inthe substrate plane. That is, by providing the ultraviolet dose with adistribution in the substrate plane, the orientation of the cholestericliquid crystal layer has a distribution corresponding to thedistribution of the ultraviolet irradiation, and therefore, a pluralityof regions in which the helical axes are aligned in different directionsare formed in the cholesteric liquid crystal layer. In order that theultraviolet dose can have such a distribution in the substrate plane,for example, only a region that is not covered with a photomask may beirradiated with ultraviolet rays. Alternatively, the ultraviolet dose inthe region having the photomask may be smaller than in the region havingno photomask. In the monomer polymerizing step, heating may be performedinstead of ultraviolet irradiation so that it has a given distributionin the substrate plane.

A reflective-plate production method of the present invention includesforming a cholesteric liquid crystal layer on a substrate, and formingan alignment layer on the substrate before the cholesteric liquidcrystal layer forming step. The alignment layer is locally formed on thesubstrate in the alignment layer forming step. Such a production methodmakes it possible to obtain the above-described reflective plate of thepresent invention having the cholesteric liquid crystal layer includinga plurality of regions in which the helical axes of the cholestericliquid crystal are aligned in different directions in the substrateplane. That is, since the orientation of the cholesteric liquid crystaldiffers between a region having the alignment layer and a region havingno alignment layer, a plurality of regions in which the helical axes arealigned in different directions are formed in the cholesteric liquidcrystal layer.

A reflective-plate production method of the present invention includesforming a cholesteric liquid crystal layer on a substrate, and formingan alignment layer on the substrate before the cholesteric liquidcrystal layer forming step. A homeotropic alignment layer and ahomogeneous alignment layer are stacked in the alignment layer formingstep. One of the homeotropic alignment layer and the homogeneousalignment layer that is formed on the front side is partially removedwith a mask. Such a production method makes it possible to obtain theabove-described reflective plate of the present invention having thecholesteric liquid crystal layer including a plurality of regions inwhich the helical axes of the cholesteric liquid crystal are aligned indifferent directions in the substrate plane. That is, since one of thehomeotropic alignment layer and the homogeneous alignment layer that isformed on the front side is partially removed with a mask, both thehomeotropic alignment layer and the homogeneous alignment layer are incontact with the cholesteric liquid crystal layer. This makes itpossible to make the orientation of the cholesteric liquid crystaldifferent between the regions in contact with the alignment layers, andto form a plurality of regions, in which the helical axes are aligned indifferent directions, in the cholesteric liquid crystal layer. Thehomeotropic alignment layer and the homogeneous alignment layer can beformed by using different kinds of polyimides, and more particularly, byusing polyimides having different side chains of polyimide molecules.

A liquid crystal device of the present invention has the above-describedreflective plate. In such a liquid crystal device, the advantages of theabove-described reflective plate are provided, and it is possible toform a thin reflective layer that can produce a reflective display thatis closer to white. A specific example is a liquid crystal device havinga liquid crystal cell in which a liquid crystal layer is held between anupper substrate and a lower substrate opposing each other and made of atransmissive substrate. A reflective layer that is capable of reflectingat least circularly polarized light that rotates in a predetermineddirection may be formed on the inner side of the lower substrate, andmay have the above reflective plate.

In this case, since the reflective layer having the reflective plate canbe made of a thin film, the thickness of the liquid crystal cell can bemade to be more uniform, and the visibility of the liquid crystal deviceis increased. In such a liquid crystal device, since the helical axes ofthe helical structures formed by the cholesteric liquid crystal in thecholesteric liquid crystal layer contained in the reflective plate arealigned in various directions in the substrate plane, the distributionof the refractive index is increased, light reflected by the cholestericliquid crystal layer can be scattered, the viewing angle of thereflective display can be increased, and there is no need orsubstantially no need to provide a separate scattering layer.

An electronic device of the present invention has the liquid crystaldevice having the above-described configuration. This can provide anelectronic device that can produce a highly visible reflective display.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic showing the partial sectional configuration of areflective plate according to an exemplary embodiment of the presentinvention;

FIG. 2 is a schematic showing the partial sectional configuration of aliquid crystal display device according to an exemplary embodiment ofthe present invention;

FIG. 3 is a schematic sectional view showing a first exemplarymodification of the configuration of a reflective plate;

FIG. 4 is a schematic sectional view showing a second exemplarymodification of the configuration of a reflective plate;

FIG. 5 is a schematic sectional view showing a third exemplarymodification of the configuration of a reflective plate;

FIG. 6 is a schematic sectional view showing a fourth exemplarymodification of the configuration of a reflective plate;

FIG. 7 is a schematic sectional view showing a fifth exemplarymodification of the configuration of a reflective plate;

FIG. 8 is a schematic sectional view showing a sixth exemplarymodification of the configuration of a reflective plate;

FIG. 9 is a schematic illustrating a production method for thereflective plate shown in FIG. 1;

FIG. 10 is a perspective view of an example of an electronic deviceaccording to the present invention;

FIG. 11 is a perspective view of another example of an electronic deviceaccording to the present invention;

FIG. 12 is a perspective view of a further example of an electronicdevice according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[Reflective Plate]

An embodiment of the present invention will be described below withreference to the drawings. In all the drawings, the proportions of thethickness, dimensions, and the like of the components appropriately varyfor easy reference.

FIG. 1 is a partial schematic sectional view showing a reflective plateaccording to an exemplary embodiment of the present invention. In areflective plate 1, an alignment layer 40 is formed on a transmissivesubstrate 13, and a cholesteric liquid crystal layer 18 serving as amain reflective layer is formed on the alignment layer 40. In this case,for example, light to be used for reflection enters from the oppositeside of the transmissive substrate 13 in the thickness direction. Thecholesteric liquid crystal layer 18 principally contains cholestericliquid crystal in which the helical alignment state is fixed, has aselective reflection property of reflecting only circularly polarizedlight that rotates in a predetermined direction, and can reflect lightwith a wavelength corresponding to the helical pitch of liquid crystalmolecules. A transmissive substrate may also be provided on the oppositeside of the transmissive substrate 13 with the cholesteric liquidcrystal layer 18 therebetween so that the cholesteric liquid crystallayer 18 serving as the main reflective layer is held between thesesubstrates.

In the cholesteric liquid crystal layer 18 serving as the mainreflective layer in the reflective plate 1 of this embodiment, thehelical axes of the helical structures formed by the cholesteric liquidcrystal are aligned in various directions in the plane of the substrate13. That is, the cholesteric liquid crystal layer 18 serving as the mainreflective layer includes a plurality of regions in which the helicalaxes of the helical structures formed by the cholesteric liquid crystalin the substrate plane are aligned in different directions, for example,a helical-axis vertically-aligned cholesteric liquid crystal region 18A,a helical-axis obliquely-aligned cholesteric liquid crystal region 18B,and a helical-axis parallel-aligned cholesteric liquid crystal region18C. More specifically, the helical axes are aligned substantiallyperpendicularly to the substrate plane in the helical-axisvertically-aligned cholesteric liquid crystal region 18A, are aligned ata predetermined angle to the substrate plane in the helical-axisobliquely-aligned cholesteric liquid crystal region 18B, and are alignedsubstantially parallel to the substrate plane in the helical-axisparallel-aligned cholesteric liquid crystal region 18C. While thehelical axes are aligned in clearly different directions among theregions and the helical axes in each region are aligned in the samedirection in the figure, in actuality, the helical axes are not alwaysaligned in clearly different directions among the regions, and thehelical axes in each region are not always aligned in the samedirection. However, as described below, in this embodiment, cholestericliquid crystal regions in which the helical axes are aligned at leastsubstantially vertically to, substantially parallel to, or at an angleto the substrate plane are formed by intentionally forming ahelical-axis-direction aligning means, or by aligning the helical axesin different directions in the substrate plane during production. Whenthe helical axis direction in each region is defined, the helical-axisvertically-aligned cholesteric liquid crystal region 18A may refer to aregion containing cholesteric liquid crystal, in which the helical axesand the substrate plane form an angle of 80° to 90°, in the substrateplane, and the helical-axis parallel-aligned cholesteric liquid crystalregion 18C may refer to a region containing cholesteric liquid crystal,in which the helical axes and the substrate plane form an angle of 0° to10°, in the substrate plane. The other region may refer to thehelical-axis obliquely-aligned cholesteric liquid crystal region 18B.

In such regions 18A, 18B, and 18C that are different in helical axisdirection, the helical pitch that is viewed from the directionperpendicular to the substrate plane differs. Therefore, color lightcomponents having different wavelengths are reflected by the regions18A, 18B, and 18C, as viewed from the side of the reflective plate 1perpendicular to the substrate plane, that is, it is possible to reflectlight containing different color light components (for example, whitelight). This cholesteric liquid crystal layer can be made to be thinnercompared with cholesteric liquid crystal layers in which the helicalaxes are aligned in the same direction, stacked so as to reflect mixedcolor light (for example, white light), and moreover, it is possible tomake the reflective plate 1 of a thin plate and to enhance the thicknessuniformity. By forming cholesteric liquid crystal regions in which thehelical pitch, viewed from the direction perpendicular to the substrateplane, is approximately 450 nm, 550 nm, and 600 nm, respectively, bluelight, green light, and red light can be reflected, and color light thatis even closer to white can be reflected.

The reflective plate 1 having the cholesteric liquid crystal layer 18 inwhich the helical axes of the cholesteric liquid crystal are aligned indifferent directions in the substrate plane, as in this embodiment, canbe produced in the following method. First, a predetermined alignmentfilm, a rubbed polyimide film in this case, is formed on a transmissivesubstrate 13, thereby obtaining an alignment layer 40. Subsequently, acholesteric liquid crystal monomer is applied onto the formed alignmentlayer 40, and is polymerized by irradiation with ultraviolet rays, asshown in FIG. 9. In this case, the alignment layer may be formed of, forexample, a homogeneous alignment layer 41. The cholesteric liquidcrystal monomer refers to a monomer that is polymerized to formcholesteric liquid crystal.

In the monomer polymerizing process shown in FIG. 9, a mask 48 islocally placed so that the ultraviolet dose has a distribution, and inthis case, the ultraviolet dose is small in the regions covered with themask 48. Therefore, in unmasked regions, helical-axis vertically-alignedcholesteric liquid crystal regions 18A are formed in which theultraviolet dose is relatively large, the cholesteric liquid crystal issufficiently aligned, and the helical axes are aligned perpendicularlyto the substrate plane. In masked regions, helical-axisobliquely-aligned cholesteric liquid crystal regions 18B (helical-axisparallel-aligned cholesteric liquid crystal regions 18C) are formed inwhich the ultraviolet dose is relatively small, the alignment of thecholesteric liquid crystal is less sufficient than in the unmaskedregions, and the helical axes are oriented in various directions.

The reflective plate 1 including the above-described cholesteric liquidcrystal layer 18 may be produced in the following method. First, apredetermined alignment film, a rubbed polyimide film in this case, isformed on a transmissive substrate 13, thereby obtaining an alignmentlayer 40. Subsequently, a cholesteric liquid crystal monomer is appliedonto the formed alignment layer 40 at an isotropic temperature, issubjected to supercooling, and is polymerized by irradiation withultraviolet rays, thereby obtaining the reflective plate 1 of thisembodiment. The isotropic temperature refers to a temperature at whichcholesteric liquid crystal exists in an isotropic state, and thesupercooling refers to a process of rapidly cooling a cholesteric liquidcrystal monomer, which is placed at an isotropic temperature, to atemperature at which the cholesteric liquid crystal monomer is broughtinto an anisotropic state.

In this case, when a cholesteric liquid crystal monomer in an isotropicstate is supercooled, a part thereof still remains in the isotropicstate, and a cholesteric liquid crystal layer having an orientationdistribution can be formed by polymerizing the remaining isotropic part.Therefore, it is possible to form a plurality of regions in which thehelical axes are aligned in different directions in the cholestericliquid crystal layer. The monomer was applied at a temperature 30°higher than the isotropic temperature, and was then supercooled to atemperature 30° lower than the isotropic temperature.

[Liquid Crystal Device]

A liquid crystal device using the above-described reflective plate 1according to an embodiment will now be described with reference to thedrawings. FIG. 2 is a schematic showing a partial sectionalconfiguration of the liquid crystal device of this exemplary embodiment,and in this case, a passive-matrix reflective liquid crystal displaydevice 110 is provided as an example.

In the liquid crystal display device 110 of this embodiment, as shown inFIG. 2, a lower substrate 13 and an upper substrate 14 are placedopposed to each other with a sealing material (not shown) therebetween,and a liquid crystal layer (phase-modulation liquid crystal layer) 16made of STN (Super Twisted Nematic) liquid crystal is sealed in a spaceenclosed by the lower substrate 13, the upper substrate 14, and thesealing material. In this case, the lower substrate 13 is denoted by thesame reference numeral as that of the transmissive substrate 13 of theabove-described reflective plate 1 because they correspond to eachother.

The lower substrate 13 and the upper substrate 14 are principally madeof a transmissive material, such as glass or plastic, and a retardationfilm (quarter-wave plate) 27 and a lower polarizer 28 are formed in thatorder from the outer side of the lower substrate 13 (on the oppositeside of a liquid crystal layer 16). On the other hand, a retardationfilm (quarter-wave plate) 35 and an upper polarizer 36 are also formedin that order from the outer side of the upper substrate 14 (on theopposite side of the liquid crystal layer 16).

A cholesteric liquid crystal layer 18 serving as a main reflective layeris provided on the inner side of the lower substrate 13 (on the side ofthe liquid crystal layer 16) with an alignment layer 40 therebetween,and the cholesteric liquid crystal layer 18, the alignment layer 40, andthe lower substrate 13 are formed of those in the above-describedreflective plate 1. A color filter layer 30 including R (red), G(green), and B (blue) pigment layers 30R, 30G, and 30B is formed on thecholesteric liquid crystal layer 18. The pigment layers 30R, 30G, and30B are partitioned by a black matrix BM, each of the partitionedpigment layers forms a dot, and three dots formed by the three pigmentlayers 30R, 30G, and 30B constitute one pixel. A planarizing film(overcoat) 31 is stacked on the color filter layer 30 (pigment layers)so as to planarize the irregularities due to the color filter layer 30and the black matrix BM.

Signal electrodes 25 made of a transparent conductive film, such as ITO,extend in stripes perpendicularly to the plane of the drawing on theplanarizing film 31. Scanning electrodes 32 made of a transparentconductive film, such as ITO, extend in stripes in the right/leftdirection of the drawing on the inner side of the upper substrate 14 (onthe side of the liquid crystal layer 16). The regions at which theseelectrodes 25 and 32 intersect serve as display regions, and the otherregions in which the electrodes 25 and 32 do not intersect serve asnon-display regions with the black matrix BM.

The upper polarizer 36 only transmits linearly polarized light that ispolarized in one direction (the lateral direction of the drawing in thisembodiment), and the retardation film 35 converts the linearly polarizedlight passing through the upper polarizer 36 into circularly polarizedlight. Therefore, the upper polarizer 36 and the retardation film 35function as upper-substrate-side circularly-polarized-light incidentmeans. The lower polarizer 28 only transmits linearly polarized lightthat is polarized in one direction (in the lateral direction of thedrawing in this embodiment), and the retardation film 27 converts thelinearly polarized light passing through the lower polarizer 28 intocircularly polarized light. Therefore, the lower polarizer 28 and theretardation film 27 function as a lower-substrate-sidecircularly-polarized-light incident device. While light to be used fordisplay is external light, such as solar light or illumination light, inthe description of this exemplary embodiment, a semi-transmissivereflective liquid crystal device that admits backlight from the lowerpolarizer 28 may be used.

In the liquid crystal layer 16, liquid crystal molecules are aligned inthe up/down direction of the drawing (perpendicularly to the substrateplane) in a state in which a voltage higher than or equal to thethreshold is applied between the scanning electrode 25 and the signalelectrode 32 (a selective-electric-field applied time), and are alignedin the right/left direction of the drawing (parallel to the substrateplane) in a state in which a voltage lower than or equal to thethreshold is applied therebetween (a non-selective-electric-fieldapplied time). Here, the “selective-electric-field applied time” and the“non-selective-electric-field applied time” means “the time in which thevoltage applied to the liquid crystal layer is lower than the thresholdvoltage of the liquid crystal” and “the time in which the voltageapplied to the liquid crystal layer is higher than or equal to thethreshold voltage of the liquid crystal,” respectively. In such a liquidcrystal layer 16, the phase of incident light can be modulated dependingon the application of a selective electric field. That is, in thisembodiment, incident circularly polarized light can be transmitted ascircularly polarized light which rotates in the same direction as thatat the incidence without modulating the phase thereof when a selectiveelectric field is applied, and incident circularly polarized light canbe transmitted as circularly polarized light that rotates in thedirection reverse to that at the incidence after modulating the phasethereof when a non-selective electric field is applied.

The cholesteric liquid crystal layer 18 has the same structure as thatin the reflective plate 1 shown in FIG. 1, and the helical axes of thehelical structures formed by cholesteric liquid crystal are aligned invarious directions in the substrate plane. Therefore, color light thatis closer to white light is reflected. Moreover, since the cholestericliquid crystal layer 18 itself can be made of a thin film, the thicknessof the liquid crystal cell in which the liquid crystal layer 16 is heldbetween the substrates 13 and 14 can be made to be more uniform, and thereliability of the liquid crystal device is thereby increased.Furthermore, since the distribution of the refractive index increases inthe cholesteric liquid crystal layer 18, light that is reflected by thecholesteric liquid crystal layer 18 can be scattered, the viewing anglefor the reflective display can be increased, and it is unnecessary toprovide a separate scattering layer.

A description is provided below of a display mechanism in the liquidcrystal display device 110 of this embodiment. External light enteringthe liquid crystal display device 110 through the upper polarizer 36 andthe retardation film 35 is converted into clockwise circularly polarizedlight, and enters the liquid crystal layer 16. When a voltage is appliedbetween the scanning electrode 25 and the signal electrode 32(selective-electric-field applied time), the liquid crystal layer 16 isin an ON state, and transmits the clockwise circularly polarized lightunchanged. When a voltage is not applied between the scanning electrode25 and the signal electrode 32 (non-selective-electric-field appliedtime), the liquid crystal layer 16 is in an OFF state, and transmits theclockwise circularly polarized light while converting the light intocounterclockwise circularly polarized light.

A component having a predetermined wavelength of the clockwisecircularly polarized light passing through the ON-state liquid crystallayer 16 is absorbed by the color filter layer 30. For example, awavelength of color light serving as a complimentary color of R (red) isabsorbed in the pigment layer 30R corresponding to R (red), a wavelengthof color light serving as a complimentary color of G (green) is absorbedin the pigment layer 30G corresponding to G (green), and a wavelength ofcolor light serving as a complimentary color of B (blue) is absorbed inthe pigment layer 30B corresponding to B (blue). Therefore, for example,the wavelength of clockwise circularly polarized light passing throughthe pigment layer 30R corresponding to R (red) is approximately 600 nmto 650 nm.

The clockwise circularly polarized light that becomes color light with awavelength in a specific wavelength region by passing through the colorfilter layer 30 is reflected by the cholesteric liquid crystal layer 18.In this case, the rotating direction is unchanged before and afterreflection, and the reflected clockwise circularly polarized light isused for display after passing again through the color filter layer 30,the liquid crystal layer 16, the upper substrate 14, the retardationfilm 35, and the upper polarizer 36. During thenon-selective-electric-field applied time of the liquid crystal layer16, counterclockwise circularly polarized light enters the reflectivelayer 18. The counterclockwise circularly polarized light is notreflected by the reflective layer 18, passes therethrough toward thelower substrate 13, and is absorbed by the lower polarizer 28.Therefore, the counterclockwise circularly polarized light is not usedfor display.

[Modifications of Reflective Plate]

Modifications of the reflective plate of this embodiment are describedbelow. A helical-axis-direction aligning device to align the helicalaxes of cholesteric liquid crystal in different directions in thesubstrate plane among the regions is principally described in themodifications. Components that are the same as those in the reflectiveplate shown in FIG. 1 are denoted by the same reference numerals, anddescriptions thereof are omitted. The following reflective plates arealso applicable as a main reflective layer including the cholestericliquid crystal layer 18 of the liquid crystal display device 1 shown inFIG. 2.

FIG. 3 is a schematic sectional view showing the structure of areflective plate 121 in accordance with a first exemplary modification.In the reflective plate 121, an alignment layer 40 is locally formed ona transmissive substrate 13 inside the substrate plane. Morespecifically, homogeneous alignment layers 41 are formed in a matrix,and the alignment layer 40 functions as the helical-axis-directionaligning device.

In this case, in the regions in which the homogenous alignment layers 41are formed (homogenous-alignment-layer forming region), the helical axesof the cholesteric liquid crystal are aligned substantiallyperpendicularly to the substrate plane, and helical-axisvertically-aligned cholesteric liquid crystal regions 18A are formed inthese regions. On the other hand, in the regions in which the homogenousalignment layers 41 are not formed (homogenous-alignment-layernon-forming region), the helical axes of the cholesteric liquid crystaltilt at a predetermined angle to the substrate plane, or are alignedsubstantially parallel to the substrate plane, and helical-axisobliquely-aligned cholesteric liquid crystal regions 18B and/orhelical-axis parallel-aligned cholesteric liquid crystal regions 18C areformed in these regions. By thus forming the alignment layers in theportions of the substrate plane, a plurality of regions in which thehelical axes are aligned in different directions can be formed in acholesteric liquid crystal layer 18.

FIG. 4 is a schematic sectional view showing the structure of areflective plate 122 as a second modification. In this reflective plate122, homogeneous alignment layers 41 and homeotropic alignment layers 42coexist as an alignment layer 40 on a transmissive substrate 13. Morespecifically, the homogeneous alignment layers 41 and the homeotropicalignment layers 42 are alternately formed in the same plane, and thealignment layer 40 including the homogeneous alignment layers 41 and thehomeotropic alignment layers 42 functions as a helical-axis-directionaligning device.

In this case, the helical axes of cholesteric liquid crystal are alignedsubstantially perpendicularly to the substrate plane in the regions inwhich the homogeneous alignment layers 41 are formed, and helical-axisvertically-aligned cholesteric liquid crystal regions 18A are formed inthese regions. On the other hand, the helical axes of the cholestericliquid crystal are aligned parallel to the substrate plane in theregions in which the homeotropic alignment layers 42 are formed, andhelical-axis parallel-aligned cholesteric liquid crystal regions 18C areformed in these regions. The helical axes of the cholesteric liquidcrystal tilt at a predetermined angle to the substrate plane in theregions in which the homeotropic alignment layers 42 are formed or nearthe boundaries between the alignment layers 41 and 42, and helical-axisobliquely-aligned cholesteric liquid crystal regions 18B are formed inthese regions. By thus forming the homogeneous alignment layers 41 andthe homeotropic alignment layers 42 as the alignment layer in the samesubstrate plane, a plurality of regions in which the helical axes arealigned in different directions can be formed in a cholesteric liquidcrystal layer 18.

FIG. 5 is a schematic sectional view showing the structure of areflective plate 123 in accordance with a third exemplary modification.In the reflective plate 123, a homogeneous alignment layer 41 is formedon a transmissive substrate 13, and a homeotropic alignment layer 42 islocally formed on the homogeneous alignment layer 41 in the substrateplane. Therefore, in the reflective plate 123 of the third modification,the alignment layer 40 is formed of a laminated member formed of thehomogenous alignment layer 41 and the locally formed homeotropicalignment layer 42. In this case, laminated portions and non-laminatedportions of the layers 41 and 42 are formed in the laminated alignmentlayer 40 so that at least some portions of the layers 41 and 42 are incontact with a cholesteric liquid crystal layer 18, and the alignmentlayer 40 functions as a helical-axis-direction aligning device. Such alaminated alignment layer 40 can be formed by stacking the homogeneousalignment layer 41 and the homeotropic alignment layer 42, and partiallyremoving the homeotropic alignment layer 42 formed on the front sidewith a mask.

In this case, in the regions of the cholesteric liquid crystal layer 18in contact with the homogeneous layer 41, that is, in the regions inwhich the homeotropic alignment layers 42 are partially removed, thehelical axes of the cholesteric liquid crystal are aligned substantiallyperpendicularly to the substrate plane, and helical-axisvertically-aligned cholesteric liquid crystal regions 18A are formed inthese regions. On the other hand, in the regions in contact with thelocally formed homeotropic alignment layer 42, the helical axes of thecholesteric liquid crystal are aligned parallel to the substrate plane,and helical-axis parallel-aligned cholesteric liquid crystal regions 18Care formed in these regions. In the regions in contact with thehomeotropic alignment layer 42, or near the boundaries between theregions in contact with the alignment layers 41 and 42, the helical axesof the cholesteric liquid crystal tilt at a predetermined angle to thesubstrate plane, and helical-axis obliquely-aligned cholesteric liquidcrystal regions 18B are formed in these regions. By thus forming thealignment layer as a laminated member formed of the homogenous alignmentlayer 41 and the homeotropic alignment layer 42, and causing thealignment layers 41 and 42 to be in contact with the cholesteric liquidcrystal layer 18 by partially removing the homeotropic alignment layer42 using a mask, a plurality of regions in which the helical axes arealigned in different directions can be formed in the cholesteric liquidcrystal layer 18.

FIG. 6 is a schematic sectional view showing the structure of areflective plate 124 in accordance with a fourth exemplary modification.In this reflective plate 124, irregularities are formed on the surfaceof a transmissive substrate 13, for example, by embossing, and analignment layer 40, more specifically, a homogeneous alignment layer 41,is formed on the transmissive substrate 13. In this case, the alignmentlayer 40 (homogeneous alignment layer 41) also has irregularitiescorresponding to the irregularities of the transmissive substrate 13,and the alignment layer 40 (homogeneous alignment layer 41) having theirregularities functions as a helical-axis-direction aligning device. Ina cholesteric liquid crystal layer 18 of such a reflective plate 124,the helical axes of cholesteric liquid crystal placed on theirregularities of the alignment layer 40 (homogeneous alignment layer41) tilt in various directions with respect to the substrate planebecause of the irregularities, and a plurality of regions in which thehelical axes are aligned in different directions are formed in thesubstrate plane. That is, by forming irregularities on the substrateplane, at least two of a helical-axis vertically-aligned cholestericliquid crystal region 18A, a helical-axis obliquely-aligned cholestericliquid crystal region 18B, and a helical-axis parallel-alignedcholesteric liquid crystal region 18C can be formed.

FIG. 7 is a schematic that shows a reflective plate 125 in accordancewith a fifth exemplary modification in which an acrylic layer 45 isformed on a transmissive substrate 13, and irregularities are formed asa helical-axis-direction aligning device on the acrylic layer 45 so asto form irregularities on an alignment layer 40 (homogeneous alignmentlayer 41).

FIG. 8 is a schematic sectional view showing the structure of areflective plate 126 in accordance with a sixth exemplary modification.In this reflective plate 126, a homogeneous alignment layer 41 is formedas an alignment layer 40 on a transmissive substrate 13, and acholesteric liquid crystal layer 18 is formed on the homogeneousalignment layer 41. In this case, filling beads 46 serving as ahelical-axis-direction aligning means are charged in the cholestericliquid crystal layer 18, and for example, the filling rate is determinedto a rate at which the filling beads 46 do not touch.

In this case, the helical axes of cholesteric liquid crystal on thehomogeneous alignment layer 41 are aligned perpendicularly to thesubstrate plane, and are held in that direction in the regions in whichthe filling beads 46 are not charged, thereby forming helical-axisvertically-aligned cholesteric liquid crystal regions 18A. On the otherhand, in the regions in which the filling beads 46 are charged, that is,near the surfaces of the filling beads 46, the helical axes of thecholesteric liquid crystal are not held perpendicularly to the substrateplane, and instead are aligned parallel to or tilt relative to thesubstrate plane. Therefore, by filling the filling beads 46 in thecholesteric liquid crystal layer 18, a plurality of regions in which thehelical axes of the cholesteric liquid crystal are aligned in differentdirections can be formed in the cholesteric liquid crystal layer 18.

While the filling beads 46 are made of glass in the reflective plate126, they may be made of resin. The surfaces of the filling beads 46 maybe subjected to a homeotropic surface treatment, more specifically, maybe covered with a fluoric coating having high surface tension. Such acoating makes it possible to align the cholesteric liquid crystal inmore directions on the surfaces of the filling beads 46, and therefore,to more reliably form a plurality of regions in which the helical axesof the cholesteric liquid crystal are aligned in various directions.While the beads are used as fillers in this embodiment, cylindricalfibers may be used.

[Electronic Devices]

A description is provided below of an example of an electronic devicehaving the liquid crystal display device of the above embodiment.

FIG. 10 is a perspective view showing an example of a portabletelephone. In FIG. 10, reference numerals 1000 and 1001 denote a mainbody of the portable telephone, and a liquid crystal display sectionusing the above-described liquid crystal display device 110,respectively.

FIG. 11 is a perspective view showing an example of a wristwatch-typeelectronic device. In FIG. 11, reference numerals 1100 and 1101 denote awatch body, and a liquid crystal display section using theabove-described liquid crystal display device 110, respectively.

FIG. 12 is a perspective view showing an example of a portableinformation processing device, such as a word processor or a personalcomputer. In FIG. 12, reference numerals' 1200, 1202, 1204, and 1206denote an information processing device, an input section such as akeyboard, a main body of the information processing device, and a liquidcrystal display section using the above-described liquid crystal displaydevice 110, respectively.

Since the electronic devices shown in FIGS. 10 to 12 use the liquidcrystal display device 110 of the above-described embodiment, they canproduce highly visible reflective display.

The technical field of the present invention is not limited to the aboveexemplary embodiment, and various modifications are possible withoutdeparting from the scope of the present invention. For example, whilethe passive-matrix reflective liquid crystal display device is describedin the above exemplary embodiment, the present invention is not limitedthereto, and is also applicable to an active-matrix liquid crystaldisplay device. Furthermore, while the color filter layer is formed onthe inner side of the lower substrate in the above embodiment, it may beformed on the inner side of the upper substrate.

[Advantages]

As described in detail above, in the present invention, since thecholesteric liquid crystal layer in the reflective plate includes, inthe substrate plane, a plurality of regions in which the helical axes ofthe cholesteric liquid crystal are aligned in different directions, theregions can reflect color light components having different wavelengths.Therefore, the cholesteric liquid crystal layer can reflect light formedof light components of different colors (for example, white light) as awhole. For example, in a case in which the reflective plate is appliedto a reflective liquid crystal display device or the like, white lightcan be appropriately reflected for display.

Since the cholesteric liquid crystal layer is used as the mainreflective layer by itself, it can be made of a thin film, and thisenhances the uniformity of the thickness of the liquid crystal cell whenthe reflective plate is applied to a reflective layer of a reflectiveliquid crystal display device. Furthermore, since the helical axes ofthe helical structures formed by the cholesteric liquid crystal arealigned in various directions in the substrate plane in the presentinvention, the distribution of the refractive index is widened, andtherefore, reflected light can be scattered widely.

1. A reflective-plate production method, comprising: forming a cholesteric liquid crystal monomer layer on a substrate; polymerizing the cholesteric liquid crystal monomer to fix an alignment state of the helical axis of each cholesteric liquid crystal molecule; and forming an alignment layer on said substrate before said cholesteric liquid crystal monomer layer forming step and the polymerizing step, said alignment layer being locally formed on said substrate so that helical axes of cholesteric liquid crystal molecules are oriented in one direction in regions where the alignment layer is formed and in a different direction in regions where the alignment layer is not formed.
 2. A reflective-plate production method, comprising: forming a cholesteric liquid crystal monomer layer on a substrate: and polymerizing the cholesteric liquid crystal monomer to fix an alignment state of the helical axis of each cholesteric liquid crystal molecule in the cholesteric liquid crystal monomer so that helical axes of at least two cholesteric liquid crystal molecules extend in different directions with respect to a plane of the substrate.
 3. The reflective-plate production method according to claim 2, wherein the cholesteric liquid crystal monomer layer forming step includes applying a cholesteric liquid crystal monomer, said applying step including applying the cholesteric liquid crystal monomer in an isotropic state and then supercooling the applied cholesteric liquid crystal monomer.
 4. The reflective-plate production method according to claim 2, wherein the polymerizing step includes polymerizing the applied cholesteric liquid crystal monomer by ultraviolet irradiation, in said monomer polymerizing step, the ultraviolet dose having a distribution in the plane of said substrate when the ultraviolet irradiation is performed.
 5. The reflective-plate production method of claim 2, further comprising: forming an alignment layer on said substrate before said cholesteric liquid crystal monomer layer forming step, said alignment layer forming including stacking a homeotropic alignment layer and a homogeneous alignment layer, and partially removing one of said homeotropic alignment layer and said homogeneous alignment layer that is formed on the front side. 